Voltage control circuit



W. R. RAMBO Filed Oct. 19, 1945 VCLTAGE CONTROL CIRCUIT March 16, 1948.

INVENTOR WILL/AM R. RAMBO A T TORNEY I Patented Mar. 16, 1948 STATESPATENT OFFICE to the United States of America by the Secretary of War asrepresented Application ()ctober 19, 1945, Serial No. 623,420

3 Claims.

This invention relates to voltage control. More particularly it relatesto means for automatically and periodically varying the direct-currentpotential applied to specific points in a circuit such as on the variouselectrodes of electronic tubes.

In many instances it is desirable to alter the direct-current potentialof a point in an electrical or radio circuit within a predeterminedrange and in accordance with a predetermined period of variation. Onemethod of accomplishing this has been to vary such voltage by use of amotor driven potentiometer. This has grave disadvantages arising fromthe fact that a sliding contact on the potentiometer is required. Mostimportant of these disadvantages are the introduction of noise in radiocircuits, variability in results due to changes in temperature and tothe presence of oxidation and dirt, and the short life of such apotentiometer due to wear at the contacts. The use of a multivibratoreliminates the disadvantages of sliding contacts but is limited in itsuse because it has not been found practical to alter the pulse widthwithout altering the pulse repetition frequency.

It is object of the present invention to provide a periodically variablevoltage supply which eliminates sliding contacts and thus eliminates thedisadvantages inherent in them.

It is also an object of this invention to provide a condenser controlledsupply of direct-current potential derived from a primary constantdirectcurrent potential source.

It is a further object of the present invention to provide a supply ofpulsating direct-current potential from a constant direct-currentpotential source in which the pulse repetition frequency and width ofthe output pulses may be varied independently.

Other objects, features, and advantages of this invention will suggestthemselves to those skilled in the art and will become apparent from thefollowing description of the invention taken in connection with theaccompanying drawing.

Referring now to the drawing, which is a sche ic diagram of a circuitembodying the prin 1 direct-current potential. The high potenofpotentiometer R1 is connected through to the potential terminal of storoutput terminals l of this voltage supply. Between adjustable contact onpotentiometer R1 and the low potential end of the potentiometer areresistor R3 and capacitor C1 in series with each other. Parallel tocapacitor C1 and between points 0 and 7 there is connected a network ineluding a voltage divider, two gas filled diodes, and two vacuumtriodes. Normally nonconduc'ting gas filled tube N1 is connected inseries with resistor R4 between circuit points 0 and i. In series witheach other and shunting tube N1, resistors R5 and Rs are connectedbetween circuit points 6 and 8. Resistor R5 together with triode V1,resistor R7, and normally nonconducting gas filled tube N2 form anotherpath between points is and I. The plate of tube V1 is connected tocircuit point 9 between resistors R5 and Re. Resistor R7 is in thecathode lead of tube V1 being connected between gas filled tube N2 andcathode terminal l0. Variable capacitor C2 is connected to form a, pathbetween circuit point 8 and cathode terminal l0 shunting resistor R4,gas filled tube N2, and resistor R7. Vacuum tube V2 has its cathodeconnected directly to the grid of tube V1 and has a bias on its gridobtained from a voltage divider comprising resistors Ra and R9. The gridof tube V2 is connected at point H between these resistors which arethemselves connected between circuit point 8 and cathode terminal H3.The plate of tube V2 is connected to the low potential terminal 5 of theoutput terminals which are across capacitor C3 in turn shunted byresistor R10.

For operation from a 220 volt direct-current supply, at a pulserepetition frequency of in the neighborhood of 20 cycles with a peakvoltage output range of 6 to 10 volts, the following values are given byway of example: R1 10,000 ohms, R2 50,000 ohms, R3 100,000 ohms, R4100,000 ohms, R5 150,000 ohms, Rs 1 megohm, R7 5 megohms, R8 10 megohms,R9 10 megohms, R10 10 megohms, C1 .01 mid, C2 0-800 mmfd, and C3 .1 mid.It is to be understood that these values may be varied both overall andin relation to each other and depend upon the characteristics of thetubes used and the characteristics of the output potential.

Following there is a description of the manner in which this circuitoperates to produce the desired results: The position of contact 5 onpotentiometer R1 is chosen for the desired frequency of operation and,as above stated, once chosen remains fixed for that particularfrequency. A direct-current voltage is applied across points I and 2 anda portion of this voltage appears between contact 5 and the lowpotential end of potentiometer R1. This voltage charges capacitor C1through resistor R3 to the point where the break-down potential isapplied to gas filled tube N1. When this point is achieved tube N1breaks down and discharges capacitor C1. The potential across tube N1then drops, N1 is extinguished, and the cycle repeats at a frequencydetermined by values of resistor R3 and capacitor C1 and the appliedconstant direct-current voltage. Resistors R4, R5, R6, constitute avoltage divider which splits the voltage of the charge on capacitor C1in such a manner that gas filled tube N1 breaks down before gas filledtube N2 breaks down. Most of the voltage across this voltage divider isacross resistorRs. When no current is flowing through resistor R7, thereis no bias on vacuum tube V1 and the polarities are such that tube V1presents a very low resistance during the period when capacitor C1 isbeing charged.

As soon as gas filled tube N1 breaks down a potential appears acrossresistor R4 equal to the original charge on capacitor C1 less theionizing potential of gas filled tube N1. This voltage on resistor R1plus the high voltage on capacitor C2 is sufficient to break down tubeN2. Capacitor C2 slowly discharges through resistor R4, tube N2 andresistor R7. The time of discharge of capacitor C2 is determined by thecharge on that capacitor which is variable. The peak voltage to whichcapacitor C2 charges is constant so that the charge is a function of thecapacity of capacitor C2. When capacitor C2 has partially discharged,tube N2 is extinguished. Capacitor C2 cannot discharge through tube V1because polarities are wrong. It is to be noted that the potential oncapacitor C1 cannot be applied to capacitor C2 until tube N2 has beenextinguished because the discharge current through resistor R7 biasestube V1 beyond cut-ofi.

Before tube N2 breaks down the cathodes of tubes V1 and V2 are at thesame potential, and a negative cut-ofl bias is applied to tube V2 by thevoltage divider action of resistors R8 and R2, As soon as tube N2 breaksdown, the positive voltage on the cathode of V2 drops and the grid biasnow existing causes the impedance of tube V2 to be small compared withthat of resistor R2. Current fiows through resistor R2 chargingcapacitor C3. This current fiows so long as the decreasing gridpotential on tube V2 exceeds the constant cath'ode bias, that is,ionizing potential of tube N2 by the amount equal to the cut-oil. biasof the tube. Shortly after tube V2 cuts oiT, the potential on tube N2 isdecreased and tube N2 is extinguished. No current now flows in resistorR7, the cut-oif bias is removed from tube V1 and a charging potential isagain applied to capacitor C2, so that the cycle repeats itself when thevoltage on capacitor C1 has reached suflicient level.

Capacitor C3 has been discharging through resistor Rm but recharges witheach pulse the amount of charge being determined by the pulse length.The voltage on capacitor 03, that is, the output voltage depends uponthe amount of the charge and so is variable as the charge per unit timevaries with the capacity of capacitor C2. It is thus seen that byvarying the setting .of potentiometer R1 the output pulse repetitionfrequency may be varied without afiecting the pulse width and that byvaryin the capacity of capacitor C2 the output pulse width is changedwithout affecting the pulse repetition frequency.

While there has been here described what is at present considered to bethe preferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention.

What is claimed is:

1. A pulse generator of independently adjustable pulse width andfrequency comprising: a first capacitor; a main discharge circuit forsaid capacitor comprising a first discharge tube and resistor in series;means to charge said capacitor at an adjustable rate to determine thepulse frequency; an auxiliary discharge circuit for said first capacitorin parallel with said main circuit comprising controllable means and asecond resistor and discharge tube in series, said first discharge tubeand said controllable means bein connected to the same terminal of saidcapacitor; 9. second capacitor having one terminal connected betweensaid first discharge tube and resistor and the other terminal connectedbetween said controllable means and said second resistor, meansresponsive to current flow in said second resistor to prevent currentflow in said controllable means, and means to adjust the discharge rateof said second capacitor through said second resistor and discharge tubeto determine the width of the pulse discharge through said seconddischarge tube.

2. A pulse generator of independently adjustable pulse width andfrequency comprising: a first capacitor, a main discharge circuit forsaid capacitor comprising a first discharge tube and resistor in series;means to charge said capacitor at an adjustable rate to determine thepulse frequency; an auxiliary discharge circuit for said first capacitorin parallel with said main circuit comprising the plate cathode circuitof a thermionic tube and a second resistor and discharge tube in series,said first discharge tube and the plate of said thermionic tube beingconnected to the [positively charged terminal of said capacitor; asecond capacitor having one terminal connected between said firstdischarge tube and resistor and the other terminal connected between thecathode of said thermionic tube and said second resistor, the grid ofsaid thermionic tube being connected between said second resistor andsaid second discharge tube to prevent current flow in said thermionictube when current flows in said second resistor, and means to vary thedischarge rate of said second capacitor through said second dischargetube and resistor to determine the width of the pulse discharge throughsaid second discharge tube.

3. A pulse generator as in claim 2 including a thermionic output tubehaving a cathode connected between said second resistor and said seconddischarge tube, a grid connected to a voltage divider across said secondcapacitor, and a plate connected through a load impedance to a source ofpositive potential, whereby said output tube conducts only while saidsecond discharge tube is conducting and does not charge said secondcondenser.

WILLIAM R. RAMBO.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number

